Polycarbonate-based thermoplastic resin composition and process for producing the same

ABSTRACT

A polycarbonate-based thermoplastic resin composition is characterized by comprising a polycarbonate and a substantially gel-free polymer obtained by polymerizing an aromatic vinyl monomer in the presence of a polymer obtained by polymerizing a specific alkyl (meth)acrylate, an aromatic vinyl monomer, and a monomer having two or more unsaturated groups. The composition has excellent moldability (flowability, etc.) while having the intact mechanical properties (impact strength, etc.) inherent in the polycarbonate and has an excellent balance between moldability and mechanical properties. Due to the excellent balance, the composition enables size increase and thickness reduction in molded articles in various fields, especially in the field of domestic electrical appliances and housings for OA apparatuses. The composition is of great industrial value.

TECHNICAL FIELD

The present invention relates to a polycarbonate thermoplastic resincomposition which is superior in fluidity and impact strength.

BACKGROUND ART

Polycarbonates are used in various fields such as housing materials ofappliances and office automation appliances because of excellentmechanical properties such as impact strength.

However, polycarbonates have drawbacks such as low fluidity and poorprocessability.

To improve the fluidity, the molecular weight of the polycarbonatesthemselves may be decreased. However, when the molecular weight of apolycarbonate is decreased, the impact strength is lowered. In general,a styrene-butadiene-acrylonitrile copolymer is mixed to improve thefluidity, however, a large amount of the copolymer must be mixed toobtain effective fluidity and as a result, the impact strength islowered.

For the purpose of improving the balance between the fluidity and theimpact strength of polycarbonates, an experiment of adding various vinylpolymers was carried out. This experiment is roughly divided into atrial of improving the fluidity of high-molecular weight polycarbonateshaving high impact strength and low fluidity and a trial of improvingthe impact strength of low-molecular weight polycarbonates having highfluidity and low impact strength.

For example, Japanese Unexamined Patent Application, First PublicationNo. Sho 56-143239, Japanese Unexamined Patent Application, FirstPublication No. Hei 1-65461, and Japanese Unexamined Patent Application,First Publication No. Hei 1-268761 describe that the impact strength ofpolycarbonates is improved by adding a polymer containing an alkylacrylate rubber.

However, the resin composition thus obtained has insufficient fluidityand insufficient impact strength.

Also Japanese Unexamined Patent Application, First Publication No. Sho62-138514 describes that the fluidity of polycarbonates is improved byadding a polymer comprising an aromatic vinyl monomer and methylmethacrylate.

However, the resin composition thus obtained has low impact strength.

Japanese Unexamined Patent Application, First Publication No. Hei5-140435 describes that the fluidity of polycarbonates is improved byadding a low molecular weight polymer comprising an aromatic vinylmonomer and all alkyl acrylate.

However, since this low-molecular weight polymer contains a large amountof soft components, the polymer is sticky and has poor handlingproperties, such that blocking is likely to occur. Moreover, when testpieces have a large thickness, the impact strength is lowered.

Japanese Unexamined Patent Application, First Publication No. Hei1-268761 describes that the addition of a high-molecular weight alkylmethacrylate polymer is effective to prevent sagging of polycarbonatesduring extrusion molding.

However, the addition is not effective to improve the fluidity.

Japanese Unexamined Patent Application, First Publication No. Hei11-181197 describes that polycarbonates are superior in fluidity, heatresistance, transparency, and odors/fumes when a low-molecular weightaromatic vinyl polymer having a solubility parameter of more than 9.3and less than 11.5 is added.

However, the resin composition thus obtained has low impact resistance.

As described above, although an experiment of adding various vinylpolymers has been carried out in the prior art, no experiment has eversucceeded in improving the balance between the fluidity and the impactstrength of polycarbonates.

DISCLOSURE OF INVENTION

The present invention has been made to solve the above problems and theobject thereof is to improve processability (for example, fluidity)without impairing the excellent mechanical characteristics (for example,impact strength) unique to polycarbonates, and to provide apolycarbonate thermoplastic resin composition having an excellentbalance between both characteristics.

The present inventors have intensively studied to achieve the aboveobject and found it very effective to add a specific polymer obtained bytwo-stage polymerization to polycarbonates, and thus the presentinvention has been completed.

The polycarbonate thermoplastic resin composition of the presentinvention comprises: a polymer (A), which contains substantially no gel,obtained by polymerizing an aromatic vinyl monomer (a-4) in the presenceof a polymer obtained by polymerizing 15 to 100% by weight of an alkyl(meth)acrylate (a-1) whose an alkyl group has 2 to 20 carbon atoms, 85to 0% by weight of an aromatic vinyl monomer (a-2), and a monomer (a-3)having two or more unsaturated groups and a polycarbonate (B).

The alkyl (meth)acrylate (a-1) is preferably at least one monomerselected from the group consisting of ethyl (meth)acrylate, butyl(meth)acrylate and 2-ethylhexyl (meth)acrylate.

The weight-average molecular weight of the polymer of (a-1). (a-2), and(a-3) is preferably 300,000 or less.

The method for manufacturing the polycarbonate thermoplastic resincomposition comprises:

-   -   a first-stage polymerization step of polymerizing 15 to 100% by        weight of an alkyl (meth)acrylate (a-1) whose alkyl group has 2        to 20 carbon atoms, 85 to 0% by weight of an aromatic vinyl        monomer (a-2), and a monomer (a-3) having two or more        unsaturated groups,    -   a second-stage polymerization step of polymerizing an aromatic        vinyl monomer (a-4) in the presence of the polymer obtained in        the first-stage polymerization step, and    -   a mixing step of mixing the polymer (A) obtained in the        second-stage polymerization step with a polycarbonate (B).

In the present invention, “(meth)acrylate” means “at least acrylate ormethacrylate”.

BEST MODE FOR CARRYING OUT THE INVENTION

The polymer (A) used in the present invention is obtained by two-stagepolymerization. In the first-stage polymerization, an alkyl(meth)acrylate (a-1) an aromatic vinyl monomer (a-2), and a monomer(a-3) having two or mole unsaturated groups are polymerized.

In the second-stage polymerization, an aromatic vinyl monomer (a-4) ispolymerized in the presence of the polymer obtained in the first-stagepolymerization.

The alkyl (meth)acrylate (a-1) used in the present invention has analkyl group having 2 to 20 carbon atoms. The alkyl group may has eithera straight chain or a branched chain. Specific examples of the alkyl(meth)acrylate include ethyl (meth)acrylate, butyl (meth)acrylate,2-methylbutyl (meth)acrylate, 3-methylbutyl (meth)acrylate, hexyl(meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate,2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, lauryl,(meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl(meth)acrylate, and eicosyl (meth)acrylate. These alkyl (meth)acrylatescan be used alone, or two or more kinds of them can be used incombination.

Taking account of the fluidity and cost of the resin composition, ethyl(meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate lauryl(meth)acrylate, tridecyl (meth)acrylate, and stearyl (meth)acrylate arepreferred. Among these, ethyl (meth)acrylate, butyl (meth)acrylate, and2-ethylhexyl (meth)acrylate are more preferred.

Specific examples of the aromatic vinyl monomer (a-2) used in thepresent invention include styrene, α-methylstyrene, p-methylstyrene,α-methyl-p-methylstyrene, p-methoxystyrene, o-methoxystyrene,2,4-dimethylstyrene, chlorostyrene, and bromostyrene. These aromaticvinyl monomers can be used along, or two or more kinds of them can beused in combination. Taking account of the fluidity and cost of theresin composition, styrene, α-methylstyrene, and chlorostyrene arepreferred.

Although the aromatic vinyl monomer (a-2) is not necessarily essential,the appearance of the molded article can be improved by using thearomatic vinyl monomer.

Specific examples of the monomer having two or more unsaturated groups(a-3) used in the present invention include allyl (meth)acrylate,triallyl cyanurate, triallyl isocyanurate, ethylene glycoldi(meth)acrylate, propylene glycol di(meth)acrylate. 1,3-butylene glycoldi(meth)acrylate, and 1,4-butylene glycol di(meth)acrylate. Takingaccount of the fluidity of the resin composition, monomers having two ormore unsaturated groups with different reactivities for example, allyl(meth)acrylate, triallyl cyanurate, and triallyl isocyanurate arepreferred. Triallyl cyanurate and triallyl isocyanurate have three allylgroups. The reactivity of the allyl group which is reacted first isdifferent from that of the allyl groups which are reacted second andthird.

In the case of polymerizing the monomers (a-1) (a-2) and (a-3), one, ortwo or more kinds of copolymerizable compounds such as: α-olefin such asethylene or propylene; an ester of vinyl alcohol such as vinyl acetate;a compound having an epoxy group such as vinyl glycidyl ether or allylglycidyl ether; a dicarboxylic anhydride such as maleic anhydride; avinyl monomer having a functional group such as an amino group, hydroxylgroup, mercapto group carboxylic acid group, carboxylic anhydride,dicarboxylic acid, halogen group, or halogenated carbonyl; and(meth)acrylic acid or methyl (meth)acrylate can be used in combinationin the amount of 50% by weight or less based on the total polymerizationcomponent.

The aromatic vinyl monomer (a-4) of the present invention may be thesame as that of the monomer (a-2).

In the case of polymerizing the monomer (a-4), one, or two or more kindsof copolymerizable compounds such as: alkyl (meth)acrylate such as(meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate,tridecyl (meth)acrylate, or stearyl (meth)acrylate; α-olefin such asethylene or propylene; an ester of vinyl alcohol such as vinyl acetate;a compound having an epoxy group, such as glycidyl (meth)acrylate, vinylglycidyl ether, or allyl glycidyl ether; a dicarboxylic anhydride suchas maleic anhydride; and a vinyl monomer having a functional group suchas an amino group, hydroxyl group, mercapto group, carboxylic acidgroup, carboxylic anhydride, dicarboxylic acid, halogen group, orhalogenated carbonyl can be used in combination in the amount of 50% byweight or less based on the total polymerization component.

In the first-stage polymerization, the proportion of the alkyl(meth)acrylate (a-1) is from 15 to 100% by weight and the proportion ofthe aromatic vinyl monomer (a-2) is from 85 to 0% by weight. Takingaccount of the impact strength of the resin composition, the proportionof the alkyl (meth)acrylate (a-1) is preferably from 25 to 100% byweight and the proportion of the aromatic vinyl monomer (a-2) ispreferably from 75 to 0% by weight. Taking account of the appearance ofthe molded resin composition, the proportion of the alkyl (meth)acrylate(a-1) is more preferably from 25 to 95% by weight and the proportion ofthe aromatic vinyl monomer (a-2) is more preferably front 75 to 5% byweight; the proportion of the alkyl (meth)acrylate (a-1) is mostpreferably, from 25 to 85% by weight and the proportion of the aromaticvinyl monomer (a-2) is most preferably from 75 to 15% by weight.

The polymer (A) contains substantially no gel. As used herein, gelrefers to a polymer or polymer particles having a three-dimensionalnetwork. To confirm that the polymer (A) does not contain a gel, forexample, the following means is used. It can be said that the polymer(A) contains substantially no gel if there exists a liquid whichdissolves the polymer (A).

In the first-stage polymerization, the amount of the monomer having twoor more unsaturated groups (a-3) is within a range where the polymer (A)contains substantially no gel, and is preferably from 0.001 to 10 partsby weight based on 100 parts by weight of the total amount of themonomers (a-1) and (a-2). Although the addition of the monomer (a-3)improves the appearance of the molded resin composition, when the amountof the monomer is too large or the reactivity is too high, a gel isformed in the polymer and the fluidity of the resin composition islowered. The use of a chain transfer agent in the first-stagepolymerization is preferred because it suppresses the formation of agel, and the amount is preferably from 0.001 to 10 parts by weight.

The proportion of the polymer of the first stage and the proportion ofthe aromatic vinyl monomer (a-4) in the second-stage polymerization maybe appropriately set, if necessary, and is not specifically limited inthe present invention. Based on the amount of the respective monomers,the total amount of the monomers (a-1) and (a-2) is preferably from 1 to90% by weight and the amount of the monomer (a-4) is preferably from 99to 10% by weight while the total amount of the monomers (a-1) and (a-2)is more preferably from 5 to 60% by weight and the amount of the monomer(a-4) is more preferably from 95 to 40% by weight. When the proportionof the aromatic vinyl monomer (a-4) is appropriately increased, thestickiness of the polymer (A) is suppressed, and thus blocking can besatisfactorily prevented and handling properties can be improved. Whenthe proportion of the aromatic vinyl monomer (a-4) is appropriatelydecreased, the impact strength of the resin composition is moreimproved.

After the completion of the first-stage polymerization, theweight-average molecular weight of the polymer is preferably from 3,000to 300,000 and more preferably from 3,000 to 50,000, taking account ofthe processability of the resin composition. After the completion of thesecond-stage polymerization, the weight-average molecular weight of thepolymer (A) is preferably from 3,000 to 1,000,000 and more preferablyfrom 3,000 to 600,000.

The molecular structure of the polymer (A) is not specifically limitedas long as the polymer contains substantially no gel. The polymer mayhave a straight-chain, comb, branched, star-shaped, or cascade-shapedmolecular structure.

The two-stage polymerization method for obtaining the polymer (A) is notspecifically limited and various conventionally known polymerizationmethods can be used such as radical polymerization, anionpolymerization, and cation polymerization in a bulk, solution, emulsion,or suspension system. In the polymerization, various conventionallyknown polymerization additives can be used such as polymerizationinitiators, polymerization catalysts, chain transfer agents, molecularweight modifiers, organic solvents, dispersion mediums, emulsifiers, anddispersants.

Examples of the polymerization initiator of the radical polymerizationinclude peroxide such as tert-butyl hydroperoxide or cumenehydroperoxide; azo initiator such as azobisisobutyronitrile; and redoxinitiator using an oxidizing agent and a reducing agent in combination.Specific examples of the redox initiator include sulfoxylate initiatorsusing ferrous sulfate, disodium ethylenediamine tetraacetate, rongalite,and hydroperoxide in combination.

Examples of the emulsifier include a nonionic emulsifier, anionicemulsifier, cationic emulsifier, and amphoteric ion emulsifier. Specificexamples of the nonionic emulsifier include polyoxyethylene alkyl ether,polyoxyethylene alkyl allyl ether,dialkylphenoxypoly(ethyleneoxy)ethanol, polyvinyl alcohol, polyacrylicacid, and alkylcellulose. Specific examples of the anionic emulsifierinclude fatty acid salts, higher alcohol sulfate silts, liquid fatty oilsulfate salts, sulfates of aliphatic amine and aliphatic amide, fattyalcohol phosphate salts, sulfonates of dibasic fatty acid esters, fattyacid amide sulfonates, alkylallyl sulfonates, and naphthalenesulfonatesof formalin condensate. Specific examples of the cationic emulsifierinclude aliphatic amine salts, quaternary ammonium salts, and alkylpyridinium salts. A specific example of the amphoteric ion emulsifierincludes alkylbetaine.

Examples of the chain transfer agent include n-octylmercaptan andtert-dodecylmercaptan.

When the first-stage polymerization is conducted by emulsion radicalpolymerization, a polymerization catalyst is optionally added to amixture of water, an emulsifier, the alkyl (meth)acrylate (a-1), thearomatic vinyl monomer (a-2), the monomer having two or more unsaturatedgroups (a-3), a polymerization initiator, and a chain transfer agent,and the mixture is polymerized at a high temperature. When the aromaticvinyl monomer (a-4) is supplied in the polymerization system after thecompletion of emulsion radical polymerization and after the first-stagepolymerization is conducted, the polymer (A) can be obtained.

In the first-stage polymerization and second-stage polymerization, themethod of supplying the respective monomers is not specifically limitedand the monomers may be supplied at one time or supplied in severalportions.

According to this emulsion polymerization, a latex of the polymer (A) isobtained and the polymer (A) is isolated and recovered by pouring thelatex into an aqueous solution of a coagulating agent. As thecoagulating agent, for example, metal salts such as calcium chloride,calcium acetate, and aluminum sulfate, and sulfuric acid can be used.

The polymer (A) may be used alone, or two or more kinds of them may beused in combination.

Typical examples of the polycarbonate (B) used in the present inventioninclude 4,4′-dioxydiarylalkane polycarbonate such as4,4′-dihydroxydiphenyl-2,2-propane (i.e. bisphenol A) polycarbonate. Themolecular weight of the polycarbonate may be appropriately set, ifnecessary, and is not specifically limited in the present invention. Theweight-average molecular weight of the polycarbonate (B) is preferablyfrom 20,000 to 100,000, and more preferably 40,000 to 70,000.

The polycarbonate (B) may be prepared by various conventionally knownmethods. For example, 4,4′-dihydroxydiphenyl-2,2-propane polycarbonateis prepared by a method of using 4,4′-dihydroxydiphenyl-2,2-propane as araw material and reacting while blowing phosgene in the presence of anaqueous alkali solution and a solvent, and a method of transesterifying4,4′-dihydroxydiphenyl-2,2-propane with a carbonate diester in thepresence of a catalyst.

The thermoplastic resin composition of the present invention is acomposition containing the polymer (A) and the polycarbonate (B)described above as a main component. The proportion of both may beappropriately decided according to desired physical properties and isnot specifically limited in the present invention. To impart asufficient effect of improving the fluidity to the polycarbonate resincomposition without deteriorating performance (for example, impactstrength) of the polycarbonate itself, the amount of the polymer (A) ispreferably within a range from 0.01 to 20 parts by weight and the amountof the polycarbonate (B) is preferably within a range from 99.99 to 80parts by weight; the amount of the polymer (A) is more preferably withina range from 0.01 to 10 parts by weight and the amount of thepolycarbonate (B) is more preferably within a range from 99.99 to 90parts by weight, based on 100 parts by weight of the total of thepolymer (A) and the polycarbonate (B).

If necessary, various conventionally known additives, stabilizers,reinforcers, inorganic fillers, and impact resistance modifiers may befurther added to the thermoplastic resin composition of the presentinvention.

After preparing a masterbatch by mixing the polymer (A) with thepolycarbonate (B) at an increased proportion of the polymer (A), adesired composition can be prepared by mixing the masterbatch with thepolycarbonate (B).

The thermoplastic resin composition of the present invention can beobtained, for example, by mixing the respective components describedabove. As the mixing method, various conventionally known mixing andkneading methods can be used. Examples thereof include methods using aHenschel mixer, Banbury mixer, single screw extruder, twin-screwextruder, twin roll, kneader, and Brabender.

Various molded articles having an excellent balance between the fluidityand the impact strength can be obtained by molding the thermoplasticresin composition of the present invention thus obtained as the rawmaterial using various conventionally known molding methods such asinjection molding, hollow molding, extrusion molding, compressionmolding, and calendering.

Concrete values of the physical properties of the thermoplastic resincomposition of the present invention may be appropriately controlled, ifnecessary, and are not specifically limited in the present invention.With respect to the fluidity, a melt viscosity as measured under themeasuring conditions of the Examples described hereinafter is preferably2,000 poise or less. With respect to the impact strength, an Izod impactstrength as measured under the measuring conditions (ASTM D256) of theExamples described hereinafter is preferably 500 J/m or more. It isconsidered that a thermoplastic resin composition having these physicalproperties has an excellent balance between the fluidity and the impactstrength.

EXAMPLES

The Examples of the present invention will be described below.

Various physical properties in the Examples and Comparative Exampleswere determined by the following procedures.

(1) Solid content

The polymerized latex was dried at 170° C. for 30 minutes and the weightwas measured, and then the solid content was determined.

(2) Weight-average molecular weight (Mw)

The weight-average molecular weight was determined by gel permeationchromatography (GPC) (chloroform as an eluent, polymethyl acrylatestandard).

(3) Melt viscosity

The melt viscosity of the resin composition vas measured by a capillarytype rheometer (manufactured by Toyo Seiki Seisaku-sho, Ltd., tinder thetrade name of Capirograph) under the conditions of a nozzle D=1 mm,L/D=10, a barrel temperature of 250° C., and a shear rate of 6.080sec⁻¹.

(4) Izod impact strength (Izd.)

In accordance with ASTM D256, the Izod impact strength was measuredunder the conditions of a thickness of a specimen with a notch of 3.2mm, a temperature of 23° C., and a humidity of 50% RH. The specimen wasmolded under the conditions of a cylinder temperature of 270° C. and amold temperature of 80° C. using an injection molding machine (IS-100,manufactured by TOSHIBA MACHINE CO., LTD.).

(5) Appearance of molded resin composition

A specimen having a size of 100×100×3 mm was molded under the conditionsof a cylinder temperature of 270° C. and a mold temperature of 80° C.using an injection molding machine (IS-100, manufactured by TOSHIBAMACHINE CO., LTD.). The resulting specimen vas visually observed. As aresult, a specimen for which laminar peeling was observed was rated“good”, while a specimen for which laminar peeling was observed only atthe gate portion was rated “slightly poor”.

<Preparation Example 1: Preparation of polymer (A-I)>

In a separable flask equipped wraith a cooling tube and a stirrer, 1.0parts by weight of sodium dodecylbenzenesulfonate and 188 parts byweight of distilled water were charged and then heated to 60° C. in awater bath under a nitrogen atmosphere. A solution prepared bydissolving 0.0004 parts by weight of ferrous sulfate, 0.0012 parts byweight of disodium ethylenediamine tetraacetate and 0.48 parts by weightof rongalite in 6 parts by weight of distilled water was added, and thena mixture of 10 parts by weight of butyl acrylate, 10 parts by weight ofstyrene, 0.2 parts by weight of allyl methacrylate, 0.2 parts by weightof n-octylmercaptan, and 0.1 parts by weight of cumene hydroperoxide wasadded dropwise over 40 minutes. After stirring for 60 minutes, thefirst-stage polymerization was completed. A small amount of the emulsionthus obtained was collected and a weight-average molecular weight (Mw)of the first-stage polymer was measured. The weight-average molecularweight was 30,000.

In this emulsion, a solution prepared by dissolving 0.0004 parts byweight of ferrous sulfate, 0.0012 parts by weight of disodiumethylenediamine tetraacetate, and 0.48 parts by weight of rongalite in 6parts by weight of distilled water was added, and then a mixture of 80parts by weight of styrene, 0.8 parts by weight of n-octylmercaptan, and0.4 parts by weight of cumene hydroperoxide was added dropwise over 140minutes. After stirring for 60 minutes, the second-stage polymerizationwas completed. The solid content of the emulsion thus obtained wasmeasured. The solid content was 32%.

The emulsion was poured into an aqueous calcium chloride solution andthe resulting precipitate was dried to obtain a polymer (A-I). Theweight-average molecular weight was 30,000.

<Preparation Example 2: Preparation of polymer (A-II)>

The same operation was conducted as in Preparation example 1, exceptthat the compositions of the first and second stages were changed asshown in Table 1, and a polymer (A-II) was obtained. The solid contentwas 33%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 3: Preparation of polymer (A-III)>

The same operation was conducted as in Preparation Example 1, exceptthat the compositions of the first and second stages were changed asshown in Table 1, and a polymer (A-III) was obtained. The solid contentwas 33%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 4: Preparation of polymer (A-IV)>

The same operation was conducted as in Preparation Example 1, exceptthat the compositions of the first and second stages were changed asshown in Table 1, and a polymer (A-IV) was obtained. The solid contentwas 32%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 5: Preparation of polymer (A-V)>

The same operation was conducted as in Preparation Example 1, exceptthat the compositions of the first and second stages were changed asshown in Table 1, and a polymer (A-V) was obtained. The solid contentwas 33%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 6: Preparation of polymer (A-VI)>

In a separable flask equipped with a cooling tube and a stirrer, 1.0parts by weight of sodium dodecylbenzenesulfonate and 194 parts byweight of distilled water were charged and then heated to 60° C. in awater bath under a nitrogen atmosphere. A solution prepared bydissolving 0.0008 parts by weight of ferrous sulfate, 0.0024 parts byweight of disodium ethylenediamine tetraacetate, and 0.96 parts byweight of rongalite in 6 parts by weight of distilled water was added,and then a mixture of 100 parts by weight of styrene, 1.0 parts byweight of n-octylmercaptan, and 0.5 parts by weight of cumenehydroperoxide was added dropwise over 180 minutes. After stirring for 60minutes, the polymerization was completed. The solid content of theemulsion thus obtained was measured. The solid content was 32%.

The emulsion was poured into an aqueous calcium chloride solution andthe resulting precipitate was dried to obtain a polymer (A-VI). Theweight-average molecular weight was 30,000.

<Preparation Example 7: Preparation of polymer (A-VII)>

The same operation was conducted as in Preparation Example 6, exceptthat the composition was changed as shown in Table 2, and a polymer(A-VII) was obtained. The solid content was 32% and the weight-averagemolecular weight was 30,000.

<Preparation Example 8: Preparation of polymer (A-VIII)>

The same operation was conducted as in Preparation Example 6, exceptthat the composition was changed as shown in Table 2, and a polymer(A-VIII) was obtained. The solid content was 32% and the weight-averagemolecular weight was 30,000. The polymer (A-VIII) was sticky and waslikely to be blocked.

<Preparation Example 9: Preparation of polymer (A-IX)>

The same operation was conducted as in Preparation Example 6, exceptthat the compositions of the first and second stages were changed asshown in Table 2, and a polymer (A-IX) was obtained. The solid contentwas 32%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 10: Preparation of polymer (A-X)>

The same operation was conducted as in Preparation Example 6 except thatthe compositions of the first and second stages were changed as shown inTable 3, and a polymer (A-X) was obtained. The solid content was 33%.After the first-stage polymerization and second-stage polymerization,the polymers were in the form of a gel insoluble in chloroform and itwas impossible to measure the molecular weight.

<Preparation Example 11: Preparation of polymer (A-XI)>

The same operation was conducted as in Preparation Example 6, exceptthat the compositions of the first and second stages were changed asshown in Table 3, and a polymer (A-XI) was obtained. The solid contentwas 32%. After the first-stage polymerization and second-stagepolymerization, the polymers were in the form of a gel insoluble inchloroform and it was impossible to measure the molecular weight.

<Preparation Example 12: Preparation of polymer (A-XII)>

The same operation was conducted as in Preparation Example 6, exceptthat the compositions of the first and second stages were changed asshown in Table 3, and a polymer (A-XII) was obtained. The solid contentwas 32%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Preparation Example 13: Preparation of polymer (A-XIII)>

The same operation was conducted as in Preparation Example 6, exceptthat the compositions of the first and second stages were changed asshown in Table 3, and a polymer (A-XIII) was obtained. The solid contentwas 33%, the weight-average molecular weight was 30,000 after thefirst-stage polymerization, and the weight-average molecular weight was30,000 after the second-stage polymerization.

<Examples 1 to 5 and Comparative Examples 1 to 9>

Polycarbonate (“S2000”, manufactured by Mitsubishi Engineering-PlasticsCorporation, weight-average molecular weight: about 50,000) and thepolymers (A-I) to (A-XIII) obtained in Preparation Examples 1 to 13 weremixed in the ratios shown in Table 1 to Table 3, and then the mixtureswere extruded under the conditions of a barrel temperature of 270° C.and a screw speed of 200rpm using a 30 mmφ twin-screw extruder (“ZSK30”,manufactured by WERNER & PFLEIDERER) to prepare thermoplastic resincompositions. The melt viscosity, the impact strength, and theappearance of the molded resulting thermoplastic resin compositions wereevaluated. The results are shown in Table 1 to Table 3.

TABLE 1 Examples 1 2 3 4 5 Abbreviations of A-I A-II A-III A-IV A-V (A)First stage BA 10 10 13 — 20 EHMA — — — 10 — St 10 10 7 10 — AMA 0.2 0.40.4 0.2 0.2 OcSH 0.2 0.4 0.4 0.2 0.2 Weight-average 30,000 molecularweight (Mw) Second stage St 80 OcSH 0.8 1.6 1.6 0.8 0.8 Weight-average30,000 molecular weight (Mw) Amount of (A) 5 (parts by weight) Amount of(B) PC 95 (parts by weight) Melt viscosity 1,800 1,700 1,400 1,800 1,900(poise) Izod impact strength 600 510 640 580 600 (J/m) Appearance goodgood good good slightly poor

TABLE 2 Comparative Examples 1 2 3 4 5 Abbreviation of (A) — A-VI A-VIIA-VIII A-IX First stage BA — 10 30 — St 100 90 70 20 MMA — — — — AMA — —— 0.2 EDMA — — — — OcSH 1.0 1.0 1.0 0.2 Weight-average 30,000 molecularweight (Mw) Second stage St — — — 80 OcSH — — — 0.8 Weight-average — — —30,000 molecular weight (Mw) Amount of (A) (parts — 5 5 5 5 by weight)Amount of (B) PC 100 95 95 95 95 (parts by weight) Melt viscosity(poise) 3,600 1,100 900 690 1,300 Izod impact strength 110 130 140 190120 (J/m) Appearance good good good laminar good peeling

TABLE 3 Comparative Examples 6 7 8 9 Abbreviation of (A) A-X A-XI A-XIIA-XIII First stage BA 10 10 10 — St 10 10 — 10 MMA — — 10 10 AMA 0.2 0.2— 0.2 EDMA 0.2 — — — OcSH — — 0.2 0.2 Weight-average molecularimpossible to 30,000 weight (Mw) measure Second stage St 80 80 80 80OcSH 0.8 0.8 0.8 0.8 Weight-average molecular impossible to 30,000weight (Mw) measure Amount of (A) (parts by weight) 5 Amount of (B) PC(parts by 95 weight) Melt viscosity (poise) 3,500 3,500 1,000 1,300 Izodimpact strength (J/m) 100 590 520 110 Appearance good good laminar goodpeeling Abbreviations in tables BA: butyl acrylate EHMA: 2-ethylhexylmethacrylate St: styrene MMA: methyl methacrylate AMA: allylmethacrylate EDMA: ethylene glycol dimethacrylate OcSH: n-octylmercaptanPC: polycarbonate<Evaluation>

As is apparent from the results shown in Table 1, in Examples 1 to 5,the, melt viscosity was 2,000 poise or less and the Izod impact strengthwas 500 J/m or more, and therefore the balance between the fluidity andthe impact strength was excellent. To sufficiently prevent poorappearance of the molded resin compositions, it was effective to use apolymer (A) containing an aromatic vinyl monomer (a-2) and a monomerhaving two or more unsaturated groups (a-3).

In Comparative Example 1, since the polymer (A) was not used and on apolycarbonate (B) was used, the fluidity was poor. In Comparativeexamples 2 to 4, since a polymer (A-VI) (A-VII), or (A-VIII) obtained bythe one-stage polymerization of an alkyl (meth)acrylate and an aromaticvinyl monomer was used, the resin compositions were inferior in impactstrength. In Comparative Example 4, the resin composition was inferiorin appearance of the molded resin composition and the handlingproperties of the polymer (A-VIII) itself. In Comparative Example 5,since a polymer (A-IX) containing no alkyl (meth)acrylate (a-1) wasused, the resin composition was inferior in impact strength. InComparative Examples 6 and 7, since a polymer (A-X) or (A-XI) of acrosslinked gel was used, the resin compositions were inferior influidity. In Comparative Example 8, since a polymer (A-XII) containingno monomer (a-3) having two or more unsaturated groups was used, theresin composition was inferior in appearance of the molded resincomposition. In Comparative Example 9, since a polymer (A-XIII)containing methyl acrylate, an alkyl group of which had few carbon atoms(one), was used in place of the alkyl (meth)acrylate) late (a-1) theresin composition was inferior in impact strength.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, it is possibleto improve processability (for example, fluidity) without impairing theexcellent mechanical characteristics (for example, impact strength) ofpolycarbonates itself and to provide a polycarbonate thermoplastic resincomposition having an excellent balance between both characteristics.

Since the thermoplastic resin composition of the present invention issuperior in balance between mechanical characteristics andprocessability, it is possible to realize large-sized and thin moldedarticles in various fields such as housings of appliances and officeautomation appliances. Therefore, its industrial value is great.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Thepresent embodiment is therefore to be considered in all respects asillustrative and not restrictive, the scope of the present inventionbeing indicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1. A thermoplastic resin composition comprising: a polymer (A), which is substantially a gel-free polymer, obtained by polymerizing an aromatic vinyl monomer (a-4) in the presence of a polymer obtained by polymerizing 15 to 100% by weight of an alkyl (meth)acrylate (a-1) whose alkyl group has 2 to 20 carbon atoms, 85 to 0% by weight of an aromatic vinyl monomer (a-2), and a monomer (a-3) having two or more unsaturated groups in the presence of a chain transfer agent; and a polycarbonate (B).
 2. The thermoplastic resin composition according to claim 1, wherein the alkyl (meth)acrylate (a-1) is at least one monomer selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
 3. The thermoplastic resin composition according to claim 1, wherein a weight-average molecular weight of the polymer obtained by polymerizing 15 to 100% by weight of an alkyl (meth)acrylate (a-1) whose alkyl group has 2 to 20 carbon atoms, 85 to 0% by weight of an aromatic vinyl monomer (a-2), and a monomer (a-3) having two or more unsaturated groups is from 3,000 to 300,000.
 4. The thermoplastic resin composition according to claim 1, wherein the aromatic vinyl monomer (a-2) is styrene.
 5. The thermoplastic resin composition according to claim 1, wherein the polymer (A) is soluble in chloroform.
 6. A method for manufacturing a polycarbonate thermoplastic resin composition, comprising: a first-stage polymerization step of polymerizing 15 to 100% by weight of an alkyl (meth)acrylate (a-1) whose alkyl group has 2 to 20 carbon atoms, 85 to 0% by weight of an aromatic vinyl monomer (a-2), and a monomer (a-3) having two or more unsaturated groups in the presence of a chain transfer agent; a second-stage polymerization step of polymerizing an aromatic vinyl monomer (a-4) in the presence of the polymer obtained in the first-stage polymerization step; and a mixing step of mixing the polymer (A) obtained in the second-stage polymerization step with a polycarbonate (B).
 7. A method for manufacturing a polycarbonate thermoplastic resin composition according to claim 6, wherein the alkyl (meth)acrylate (a-1) is at least one monomer selected from the group consisting of ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.
 8. A method for manufacturing a polycarbonate thermoplastic resin composition according to claim 6, wherein a weight-average molecular weight of the polymer obtained by polymerizing 15 to 100% by weight of an alkyl (meth)acrylate (a-1) whose alkyl group has 2 to 20 carbon atoms, 85 to 0% by weight of an aromatic vinyl monomer (a-2), and a monomer (a-3) having two or more unsaturated groups is from 3,000 to 300,000.
 9. A method for manufacturing a polycarbonate thermoplastic resin composition according to claim 6, wherein the aromatic vinyl monomer (a-2) is styrene. 